1. Technical Field
The present invention relates to a liquid crystal display device, and more particularly, to a field sequential color mode liquid crystal display device and a driving method thereof.
2. Related Art
A liquid crystal display device uses a liquid crystal display panel for displaying a desired image. The liquid crystal panel includes a plurality of pixels in a matrix arrangement. A thin film transistor is disposed in each pixel. The thin film transistor switches in accordance with a data signal to control a rotation angle of liquid crystal molecules to adjust the light transmittance of the pixel in the liquid crystal panel.
The desired image is displayed by supplying light from a backlight unit to the liquid crystal panel. The backlight unit typically uses a cold cathode fluorescent lamp (CCFL) as a light source. However, a light emitting diode (LED) has been suggested as a replacement for CCFL because an LED consumes less power. LEDs are also lightweight and bright, and very suitable for small, thin and lightweight liquid crystal display (LCD) devices.
High quality image display can be achieved using a field sequential color (FSC) mode LCD device. In a FSC driving mode LCD device, a multicolor image is displayed by sequentially operating LEDs, which displays three primary colors (red, green and blue) using an afterimage effect, without using color filters. Specifically, each frame period is divided into three periods corresponding to red, green and blue, respectively. A corresponding LED emits light during one of the three periods.
FIG. 1 shows a frame in a FSC driving mode according to the related art. Referring to FIG. 1, in the FSC driving mode, each frame period is divided into three sub-frames, corresponding to red, green and blue, respectively. For example, if a frame period is about 16.7 ms, which corresponds to a frame rate of 60 Hz, then each sub-frame is about 5.56 ms.
Each sub-frame is in turn divided into a data-writing interval DW, a liquid crystal response interval LR, and a backlight irradiating interval BL. The data-writing interval DW is about 1.69 ms depending on a thin film transistor scanning. The liquid crystal response interval LR is about 1.5 ms depending on the data writing. The backlight irradiating interval BL, which is a time for turning on the backlight for each color, is the time remaining in the corresponding subframe period after the data writing interval DW and the liquid crystal response interval LR.
Red, green and blue data signals are sequentially inputted to a liquid crystal panel in the corresponding sub-frames. Then, the corresponding red, green and blue light sources are sequentially turned on. The red, green and blue light sources are sequentially arranged below the LCD panel. Each of the light sources can be an LED or a fluorescent lamp.
As the red, green and blue light sources are sequentially turned on, color light emitted from the corresponding light sources are perceived at slightly varying locations by a user due to the sequential arrangement of the light sources. Accordingly, the red, green and blue light fail to mix, but a color break-up occurs causing each color light to be separately perceived for a short time rather than a white light. The color break-up gets worse with a user's eye motion or when displaying a moving image. Also, the FSC driving method causes color mixture distortion due to liquid crystal response delay.
FIG. 2 is a graph showing variations of the light transmittance of liquid crystal in relation to liquid crystal response time in the related art FSC driving mode LCD device. When red and green are mixed to display yellow, for example, since a green sub-frame B follows a red sub-frame A, the liquid crystal response is faster in the green sub-frame B than in the red sub-frame A. Accordingly, green light has a transmittance higher than red light. Thus, yellow shifted toward green is displayed. The color mixture distortion is more pronounced when displaying yellow.
Accordingly, there is a need for an LCD device with better mixing of the red, green and blue light sources to achieve better color display. Moreover, the LCD device should be able to prevent color break-up when displaying white. Further, the LCD should be able to display color image without a deterioration of the color image quality due to a user's eye motion or when displaying a moving image.